Case Study Challenges in Human Health Hazard and Risk Assessment of Nanoscale Silver - Safety of Nanomaterials along Their Lifecycle - page 422

BOX 19.2 NANOMATERIAL IDENTIFICATION

FOR DUMMY PRODUCTS

Name DP1(dummy product 1) DP2(dummy product 2)

Ag (silver, metallic; CAS 7440-22-4)
0.09-0.11 g/L

Ag (silver, metallic; CAS
7440-22-4) >99.9%

Active substance

Water None above 0.1%

Other constituents

Ammonium carbonate, sodium carbonate,
ammonia, tannic acid, all at <1%

None above 0.1%

Impurities

Polycrystalline (TEM) particles with an
average size of 25 nm (range 10-100 nm,
measured by DLS), negatively charged
surface (zeta potential −37 mV), coated
with PVP and carbonate

Average size 5 nm, range
2-10 nm (TEM),
spherical shape

Further identifiers
of active
substance

Wet chemistry (silver salt reduction) Laser ablation

Method of
production

“risk assessors are encouraged to consider this information as part of a regulatory
risk assessment and include a justification for how this information contributes to a
nanomaterial risk assessment (e.g., determining if the dose-response relationship is
influenced by these parameters) .” (OECD 2012)
When there is uncertainty about the appropriate degree of specificity in sub-
stance identification as it is the case for nanomaterials, definition of identity could
be either broader or narrower. Although broadening the definition—for exam-
ple with regard to particle size and size distribution or surface coating—can be
expected to improve the database available for risk assessment quantitatively, it
will inevitably cause additional uncertainty. This uncertainty results from a cur-
rently limited understanding of the impact of physicochemical properties on the
hazard properties of nanomaterials (OECD 2013). When choosing a narrower
specification of the nanosilver material there is an increased likelihood that tox-
icity data are not available for certain endpoints. In these cases, read-across of
information obtained with a similar type of nanosilver will be considered, and
the degree of uncertainty resulting from the extrapolation between materials can
be described. A recent analysis by the OECD WPMN in principle supports the
latter approach and clarified that read-across of data between nanomaterials or a
nanomaterial and its corresponding non-nanoform should be applied cautiously
and with clear scientific justification (OECD 2012). In the absence of repeated-
dose toxicity data on the nanosilver-silica composite AGS-20, for example, the
US Environmental Protection Agency (EPA) decided to use data from an oral
subacute toxicity study by Park et al. (2010) on presumably uncoated size-frac-
tionated 42 nm particles to characterize the hazard from nanosilver breaking
away from the composite. Both nanoforms of silver were regarded analogous,
and the resulting uncertainties were considered to be covered by inclusion of an